In order to increase the stability of mobile aerial work platforms or cranes during operation at a job site, it has been proposed to provide the vehicle wheels with extendable axles so that the wheels can be placed at relatively great distances transversely of the vehicle chassis to thereby increase the vehicle wheel base, the axles also being retractable toward the chassis during transit or for negotiating narrow passageways.
Heretofore, these extendable and retractable axle systems included a pair of axle beams slidably mounted in each end of a box beam integral with the vehicle chassis, the wheels and associated steering linkages being mounted on the outer ends of the axle beams. A hydraulic cylinder is operatively connected to the axle beams for sliding the beams relative to the box beam and at least one transversely extending, extensible tie rod is operatively connected to the steering linkage for each wheel. These types of extendable and retractable axle systems are disclosed in U.S. Pat. Nos. 4,039,094, dated Aug. 2, 1977; and 4,449,600, dated May 22, 1984.
While these conventional extendable and retractable axle systems have been satisfactory for their intended purpose, they have been characterized by certain disadvantages in that the extent to which the wheel base can be increased is limited by the arrangement of slidably mounting an axle beam in each end of the box beam. The extensible tie rods have to be manually pinned after the axle beams have been extended and retracted, and the hydraulic cylinder for actuating the axle beams is usually separate from the tie rod. These conventional systems require time to deploy in that the tie rod pins have to be manually set.
After considerable research and experimentation the extendable and retractable axle system of the present invention has been devised to provide a wider wheel base than heretofore provided in conventional extendable and retractable axle systems, and the hydraulic cylinder for extending and retracting the axle beams also functions as a tie rod, whereby fewer parts are employed for more quickly deploying the system than conventional systems.